Paragangliomas of the mediastinum are rare neoplasms. We report a case of a unsuspected mediastinal paraganglioma in 55-year-old man. The mediastnal tumor was accidentally discovered on a chest roentgenogram and there was no history of hypertension, sweating, flushing and headache. Surgical resection was difficult with bleeding and fluctuation of arterial blood pressure reaching up to 190/130 mmHg with tachycardia. The blood pressure was controlled with nitroglycerine and tachycardia controlled with beta-blocker. After tumor resection, hypotension was treated with dopamine and blood transfusion. Postoperative recovery was satisfactory and the patient discharged after 20 days. The diagnosis of aorticosympathetic paraganglioma was established by histologic examination.